Well cementing in permafrost

ABSTRACT

A process for cementing a string of pipe in the permafrost region of a borehole of a well wherein aqueous drilling fluid actually used in drilling the wellbore in the permafrost region of a wellbore is employed. The drilling fluid contains or is adjusted to contain from about 2 to about 16 volume percent solids. Mixing with the drilling fluid (1) an additive selected from the group consisting of lignosulfonate, lignite, tannin, and mixtures thereof, (2) sufficient base to raise the pH of the drilling fluid into the range of from about 9 to about 12, and (3) cementitious material which will harden in from about 30 to about 40 hours at 40° F. The resulting mixture is pumped into the permafrost region of a wellbore to be cemented and allowed to harden in the wellbore. There is also provided a process for treating an aqueous drilling fluid after it has been used in drilling the wellbore in permafrost, and a cementitious composition for cementing in a permafrost region of a wellbore.

BACKGROUND OF THE INVENTION

Heretofore in drilling wells through permafrost regions the drillingfluid used to drill the well has been discarded or otherwise disposed ofafter which a separate cementitious material has been pumped into thewellbore for cementing as desired. Because permafrost drilling regionsare often isolated in nature, the costs of transporting drilling fluidmaterials and cementing materials are quite high and any savings in thisarea can be substantial.

SUMMARY OF THE INVENTION

According to this invention it has been discovered that drilling fluidactually used in drilling a wellbore in permafrost can be employed as amajor constituent in the cementing materials that are employed incementing a permafrost wellbore.

By this invention the drilling fluid previously used is conserved and,therefore, replaces a substantial amount of cementing material whichwould otherwise be transported to the drill site at substantial expense.

In accordance with this invention it has been found that if the drillingfluid previously used in drilling a wellbore in permafrost contains oris adjusted to contain from about 2 to about 16 volume percent solidsbased on the total volume of the drilling fluid, the solids being anytype of solid particulate matter including drill cuttings from thedrilling operation, the drilling fluid can be recovered from thewellbore and used as the base material for building the cementitiousmixture to be used for cementing in the same or other permafrostwellbores. The used drilling fluid with required volume percent solidsis first mixed with an additive selected from the group consisting oflignosulfonate, lignite, tannin, and mixtures thereof, and sufficientbase to raise the pH of the mixture into the range of from about 9 toabout 12. At the same time as the mixing of the additive and/orthereafter, cementitious material which will harden in from about 30 toabout 40 hours depending upon the amount of additive present when heldat 40° F. is also added to the drilling fluid. If desired, a frictionreducer or dispersant can be employed to improve pumpability. Suchadditives are well known in the art. Thereafter the resulting finalmixture is pumped into the permafrost region of the wellbore which is tobe cemented and is allowed to set in the wellbore until it hardens tothe desired extent.

This invention also relates to a process for treating an aqueousdrilling fluid after it has been used in drilling a wellbore inpermafrost by following the steps outlined hereinabove.

This invention also relates to a cementitious composition for cementingpipe in a permafrost region of a wellbore which employs used aqueousdrilling fluid along with the additive, base, and cementitious materialas described above.

Accordingly, it is an object of this invention to provide a new andimproved method and composition for cementing wellbores in permafrostregions.

Other aspects, objects and advantages of this invention will be apparentto those skilled in the art from this disclosure and the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

More specifically, this invention relates to a process for cementing astring of pipe or any other desired item in the permafrost region of awellbore by recovering at least part of the aqueous drilling fluid usedin drilling a wellbore in the permafrost region, not necessarily thesame wellbore, and analyzing the thus recovered drilling fluid for itssolids content. If the solids content of the drilling fluid is alreadyin the range of from about 2 to about 16 volume percent based on thetotal volume of the drilling fluid, it is suitable for use as a base forthe cementitious material to be prepared in accordance with thisinvention. If the solids content is not within the above-noted range, itshould be adjusted to within that range by the addition of any suitableparticulate solids. The particular type of solids, e.g., sand, gravel,clay, etc., present and the size gradation of the solids is not asimportant as the total volume percent of solids present.

Once the drilling fluid with a proper solids content is obtained, thereis mixed therewith an additive selected from the group consisting oflignosulfonate, lignite, tannin, and mixtures thereof, in an amount offrom about 0.05 to about 0.4 pounds per barrel per equivalent pounds perbarrel of bentonite as determined by the methylene blue test as setforth by the American Petroleum Institute (API) RP13B Section 9. Theadditive is preferably chrome lignosulfonate. At the same time that theadditive is mixed with the drilling fluid and/or after the additive ismixed with the drilling fluid, cementitious material which will hardenin from about 30 to about 40 hours (depending on the amount oflignosulfonate present) while sitting essentially quiescent at about 40°F. is mixed with the drilling fluid in an amount of from about 50 toabout 250 pounds of cementitious material per barrel (42 gallons perbarrel) of drilling fluid plus additives. A wide variety of cementsmeeting the 30 to 40 hour at 40° F. test are available and well known tothose skilled in the art, a particularly desirable cement being onewhich is a high alumina cement. Preferably the cementitious materialemployed in this invention is a high (at least about 40 weight percent)alumina calcium aluminate cement. A particularly suitable commerciallyavailable cementitious material is fondu.

Also essentially contemperaneous with and/or after mixing of theadditive with the base drilling fluid and before, or at the same time,as the addition of the cementitious material, sufficient base is addedso that the pH of the final mixture is in the range of from about 9 toabout 12.

This final mixture is then used as the cementing material for thepermafrost wellbore and is simply pumped into the permafrost region ofthe wellbore to be cemented and allowed to set until it hardens in thewellbore. A known friction reducer can be used to improve pumpability.

Any suitable base material which is nondeleterious to the drillingfluid, additive, and cementitious material can be used such as sodiumhydroxide, calcium hydroxide, magnesium hydroxide, and the like, as willbe well known and obvious to those skilled in the art.

As would be quite obvious to those skilled in the art, the particularformulation employed with a given drilling fluid will vary widelydepending on the particular type of well being drilled and the locationof the drilling site. Generally, by following the above guidelines,drilling fluid used in drilling a wellbore through permafrost can beutilized as a major constituent in the cementing material therebysubstantially reducing the cost of cementing materials and thetransportation thereof.

This invention also relates to a process for treating an aqueousdrilling fluid after it has been used in drilling a wellbore inpermafrost wherein the drilling fluid either already contains or isadjusted to contain from about 2 to about 16 volume percent solids,comprising mixing with the drilling fluid an additive as above-describedand in amounts as above-described and then essentially contemporaneouslywith and/or subsequent to the addition of the additive or additives,mixing with the drilling fluid sufficient base or bases to raise the pHof the mixture into the range of from about 9 to about 12, and then atleast one cementitious material as described above and in amountsdescribed above.

Of course, in any embodiment of this invention if the pH is alreadywithin the range of 9 to 12, no base need be added in order to practicethis invention.

This invention also relates to cementitious composition for cementingpipe or other items in a permafrost region of the wellbore whichcomposition consists essentially of aqueous drilling fluid used indrilling through permafrost and having a solids content of from about 2to about 16 volume percent, from about 0.01 to about 1.5 weight percentbased on the total weight of the composition of an additive selectedfrom the group consisting of lignosulfonate, lignite, tannin, andmixtures thereof, and from about 8 to about 40 weight percent based onthe total weight of the composition of at least one cementitiousmaterial which will harden in from about 30 to about 40 hours at about40° F., the composition having a pH in the range of from about 9 toabout 12.

The water base of the drilling fluid is preferably essentially freshwater and not salt water or brine.

As would be obvious to those skilled in the art, various acceleratorsand/or retarders known to speed up or slow down the setting up orhardening of the cement can be employed in this invention. Further, theaddition of heat to the cement as it rests in the wellbore and/or duringor before pumping into the wellbore can be employed to speed up thesetting up time of the cementitious mixture of this invention.

Generally, this invention produces a low solids cement utilizingdrilling fluid that would otherwise be discarded.

Oftentimes conventional drilling fluids employed in permafrost regionscontain large amounts of bentonite, polymers such as high molecularweight polyacrylates, xanthan gum or other similar materials, as well assolids and fresh water. Such drilling fluid additives are tolerable informing the cementitious material of this invention.

Although a requirement of the drilling fluid used in this invention isthat it contains from about 2 to about 16 volume percent solids, it isalso desirable, but not required in the broadest aspect of thisinvention, that all or a substantial portion of the solids be no largerthan 200 mesh (U.S. Sieve Series).

EXAMPLE

Fresh water containing 8.7 volume percent (based on the volume of thewhole drilling fluid) of 200 mesh and smaller bentonitic clay solids and0.265 volume percent based on the volume of whole drilling fluid of sandwas taken from a well drilled in permafrost in Alaska. To this drillingfluid was first added six pounds per barrel of chrome lignosulfonatewith mixing. Thereafter, 1.5 pounds per barrel of sodium hydroxide andthen 130 pounds per barrel of Lafarge fondu was added. All mixing wascarried out at ambient temperature and pressure until an intimatemixture of all materials was achieved by observation. The AmericanPetroleum Institute fluid loss value for the resulting cementitiousmixture was about 10 cubic centimeters for 30 minutes. The resultingmixture hardened while setting under quiescent conditions at 40° F. inabout 40 hours. The resulting mixture was hardened into test cylinders 3inches in diameter and about 8 inches long and was tested for itselastic modulus under pressure, the pressure simulating the permafrostoverburden pressure that the cement would encounter in place of awellbore. Results were as follows:

    ______________________________________                                        Confining Pressure, PSI                                                                         Average Elastic Modulus, PSI                                ______________________________________                                        400               92,223                                                      200               77,810                                                      100               64,075                                                      ______________________________________                                    

Additional tests under the same confining pressures were conducted withsimilar cylinders and the results were:

    ______________________________________                                        Confining Pressure, PSI                                                                         Average Elastic Modulus, PSI                                ______________________________________                                        400               82,134                                                      200               74,304                                                      100               65,673                                                      ______________________________________                                    

Reasonable variations and modifications are possible within the scope ofthis disclosure without departing from the spirit and scope of thisinvention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A process for cementingin the permafrost region of a wellbore comprising recovering at leastpart of the aqueous drilling fluid used in drilling a wellbore in thepermafrost region, said drilling fluid containing from about 2 to about16 volume percent solids, mixing with said drilling fluid an additiveselected from the group consisting of lignosulfonate, lignite, tannin,and mixtures thereof in an amount of from about 0.05 to about 0.4 poundsper barrel per equivalent pounds per barrel of bentonite as determinedby the methylene blue test, essentially contemporaneous with and/orsubsequent to the addition of said additive, mixing with said drillingfluid sufficient of at least one base to raise the pH of the mixtureinto the range of from about 9 to about 12 and from about 50 to about250 pounds per barrel of at least one cementitious material which willharden in from about 30 to about 40 hours at about 40° F., pumping theresulting final mixture into the permafrost region of the wellbore to becemented, and allowing said mixture to harden in said wellbore.
 2. Aprocess according to claim 1 wherein said additive is chromelignosulfonate and said base is sodium hydroxide.
 3. A process accordingto claim 2 wherein said cementitious material is high in alumina calciumaluminate.
 4. A process according to claim 2 wherein said cementitiousmaterial contains a substantial amount of fondu cement.
 5. A processaccording to claim 1 wherein said cementitious material is high inalumina.
 6. A process according to claim 1 wherein said cementitiousmaterial contains a substantial amount of fondu cement.
 7. A process fortreating an aqueous drilling fluid after it has been used in drilling awellbore in permafrost, said drilling fluid containing from about 2 toabout 16 volume percent solids, comprising mixing with said drillingfluid an additive selected from the group consisting of lignosulfonate,lignite, tannin, and mixtures thereof in an amount of from about 0.05 toabout 0.4 pounds per barrel per equivalent pounds per barrel ofbentonite as determined by the methylene blue test, essentiallycontemporaneous with and/or subsequent to the addition of said additive,mixing with said drilling fluid sufficient of at least one base to raisethe pH of the mixture into the range of from about 9 to about 12 andfrom about 50 to about 250 pounds per barrel of at least onecementitious material which will harden in from about 30 to about 40hours at about 40° F.
 8. A process according to claim 7 wherein saidadditive is chrome lignosulfonate and said base is sodium hydroxide. 9.A process according to claim 8 wherein said cementitious material ishigh in alumina calcium aluminate.
 10. A process according to claim 8wherein said cementitious material contains a substantial amount offondu cement.
 11. A process according to claim 7 wherein saidcementitious material is high in alumina.
 12. A process according toclaim 7 wherein said cementitious material contains a substantial amountof fondu cement.